Method of producing organic dhsocyanates



Patented June 1, 1954 METHOD OF PRODUCING ORGANIC DIISOCYANATES Robert J. Slocombe, Dayton, Ohio, and James H.

Saunders, Anniston, Ala., assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Serial No. 264,633

No Drawing. Application January 2, 1952,

11 Claims. 1

This invention relates to an improvement in the method of producing organic diisocyanates.

I-Ieretofore, organic diisocyanates boiling within the range of about 70 C. to about 175 C. at a pressure of about to about mm. of mercury have been prepared by reacting phosgene with the corresponding primary diamines in the presence of relatively low boiling inert organic solvents to form an intermediate reaction product which was then treated with additional quantities of phosgene to form the corresponding diisocyanate. The crude product thus obtained was treated with an inert gas such as nitrogen, natural gas, etc. to remove hydrogen chloride and unreacted phosgene, whereupon the degassed product was distilled to separate the solvent from the diisocyanate.

As a modification of the above method, the above diisocyanates have been prepared by first forming the primary amine hydrochloride salt, slurrying the salt in a relatively low boiling inert organic solvent and then treating the slurry with phosgene to convert it into a crude solution of the corresponding diisocyanate. This solution was then treated in the manner indicated in the preceding paragraph to degas same, and separate the solvent from the diisocyanate product.

The above methods have enjoyed substantial commercial success, but they are subject to the disadvantage of producing excessively low yields of organic diisocyanates due to the difficulty encountered in recovering these products. For. example, when the inert organic solvent and the major portion of the diisocyanate are removed by distillation, a substantial amount of byproduct is produced as a result of polymerization and this by-product both consumes and entraps considerable quantities of the desired product. Moreover, if the distillation temperature is raise-. in an efiort to remove the residual diisocyanate from the by-product, the residue solidifies to a brittle mass which presents operational problems since it can be removed from the reactor or still pot only with considerable difficulty.

It is an object of the instant invention to overcome the above disadvantages and provide a new method which permits more efiicient recovery of the organic diisocyanates with the result that the overall yield of these products is substantially increased.

In accordance with the present invention, the crude solution of organic diisocyanate obtained bythe above methods is subjected to distillation to successively separate the major portion of the low boiling inert organic solvent and the diisocyanate, leaving a residue containing a relatively small amount of the above diisocyanate. This residue is incorporated with a plasticizer of the type hereinafter described and the resulting product heated to distill the diisocyanate. As a modification of this technique, the plasticizer may be directly added to the crude solution or organic diisocyanate and the mixture fractionally distilled to successively separate the low boiling solvent and diisocyanate.

The plasticizer employed in the above operations may be one or more polynuclear hydrocarbons or halogenated aromatic derivatives thereofv which boil at a temperature of about 270 C. to about 400 C. at atmospheric pressure. Illustrative examples of these are o-terphenyl, mterphenyl, p-terphenyl, mixtures of two or more terphenyls, hydrogenated terphenyl mixtures such as disclosed and claimed in Patent 2,364,? 19, chlorinated biphenyl containing from 21% to 62% C1, the chlorinated mixture of biphenyl and 40% distilled high boiler containing about 65% Cl, chlorinated distilled high boiler containing 60% C1 and chlorinated isomeric terphenyl mixtures containing 42% Cl. In fact, any of the chlorinated diaryl mixtures boiling within the above range which are disclosed and claimed in Patent 1,892,400 to Swann Research, Inc. may be used.

For a complete understanding of the present invention, reference is made to the following specific examples. The parts are by weight.

Example I Metatolylene diamine was reacted with phosgene in the presence of orthodichlorobenzene to form a slurry of an intermediate reaction product whichjwas treated with additional amounts of phosgene to convert it into a crude solution of metatolylene diisocyanate. This solution was treated with natural gas to eliminate hydrogen chloride and unreacted phosgene and then sub jected to vacuum distillation to remove the above solvent and substantial amounts of the above diisocyanate, leaving a black glassy residue which was solid at room temperature.

parts of the above residue was heated'to C. with stirring to convert it into the molten state, whereupon it was allowed to cool to room temperature. The cooled product was then reheated to a temperature of about 152 C. and while under a pressure of about 20. mm. of mercury in an eiiort to efiect distillation and recovery of the entrapped diisocyanate. However, the residue merely swelled and frothed with. the

liberation of much phosgene but no distillate was recovered.

4 The foregoing Examples (III and IV) clearly illustrate that the use of a high boiling plasticizer efiects a substanial improvement in the re- Erample II covery of metatolylene dusocyanate as compared 100 parts of the black glassy residue referred to 5 with that obtainable with a, low boiling solvent. in Example I and 50 parts of a plasticizer 0011- In order to further illustrate suitable operatsisting of a chlorinated mixture of isomeric tering conditions of the instant invention, referphenyls containing 42% chlorine were mixed enceis made to the following table.

Plastlclzer Percent Yield 01 Re rar the? their tittttititi Temp., C. Type Parts Based on Residue 250 4 150 Chlorinated Isomeric Ter- 9.2

phenyl Mixture Containing 42% Chlorine. 250 4 170 do 10 23.0 250 4 10 23.6 250 i 23.4 250 4 s 20.6 250 4 10 32.5 500 2 10 13.2 500 2 10 13.3

and heated to melt the mixture completely, The residues in the above runs were prepared whereupon the molten product was cooled with by the method described in Example I, but in the stirring to room temperature, Then, the cooled case of runs 1-6 inclusive orthodichlorobenzene product was subjected to distillation, at a still was removed to the extent of about 45% by weight pot temperature of about 162 C. and a pressure of the crude solution of metatolylene diisocyanate. of 5.0-5.5 mm. of mercury, w ng was The above results indicate in the case of metastopped as a result of solidification of the residue. tolylene diisocyanate that a temperature of about 19.5 parts of metatolylene diisoeyanate was obl-60 C., about 4% by weight of plasticizer and tained as a distillate in a yield corresponding to a pressure of about 4 mm. of mercury produce the 19.5% of theory, basis Weight of original residue. best yields based on the residue charged to the The above two examples show that the use of still pot. a plasticizer of the above type facilitates distilla- Th method of th in tant i nti i aption of the residue and at the same time markedly plieable t t production and recovery of increases the yield of the desired d va a e ganic diisoeyanates which boil at a temperature of about 70 C. to about 1'75 0. while under a Emmple MI pressure of from 10 to 20 mm. of mercury. Il- A residue consisting f about 5 parts of lustrative examples of these are ethylene diisometatolylene diisocyanate and 42 parts of inolanatoy p py diisooyonato, y ne diisoactive material was prepared by the method W amrlsne d cya ate, hexamethylene described in Example I. To 78 parts of this residiisocyanate, to y e diisooyanobos, Chlorodue there was added 40 parts of orthodichloror p enylene diisocy mobaphonylone d is benzene to yield a mixture containing about 36 6379113136 and paraphenylono iisocyanate. parts of metatolylene diisocyanate, about 37.5 The p ci r oi the ins ant invention are parts of orthodichlorcbenzene and about 26.5 employed in on amount C p di g to about parts of inactive mafierial to abOut by Weight based on the Cu- 290 parts of the mixture prepared in t above isocyanate content of the crude organic solvent manner was heated and distilled under a pressolution f this product o e spec fica y, h sure of about 7 mm. of mercury, usin a still pot e employed in an amount Corresponding to temperature of about 193 C. and about 128.0 about o about by Weight and Within parts of a distillate was collected having the folthese limits about 0 about y Weight is lowing composition. l H

Parts The low boiling solvents of the prior art re- Metatolylene diisgcyanate 31. 8 ferred to above h vin boiling points which do orthodicmombenzene 3.00 not exceed 255 C. at atmospheric pressure. Inactive t mu .32 Typical examples of these are benzene, chloro- The recovery of the metatolylene diisocyanati 2:22:32: gg gfiggggf i gggg g 3S2: 1:3, obtained 11} the abcwe. f f amoj'mted to F'g chloride, tetrachloroethylene, trichloroethylene, of t 'i basls t a welght of resl ue tetrachloroethane, trichlorobenzene, decahydrobefoie addition or oithodichloi obenzene. naphthalene, tetrahydronaphthalene, amylben; zene, p-cymene, o-cymene, m-cymene, n-dodecyl- Example IV benzene, naphthalene, n-heptylcyclopentane and 300 parts of the residue employed in Example bjphenyL III and 100 parts of the plasticizer used in EX- h above descriptign and examples are p e II Were melted together and subl'ootod to tended to be illustrative only. Any modificadisfiiilation, using a Still D tomporotorfi of about tion or variation therefrom which conforms to d a pressure f ab 14 mm. f e the spirit of the invention is intended to be incu y. This resulted in the promotion of 159 eluded within the scope of the claims. parts of a distillate containing about 62.6 parts t We claim; of metatolylene diisocyanate which corresponds 1 In t method of producing Qrgamc m to a yield of about 33.4% of theory, basis Original cyanates boiling from about 70 C. to about C.

weight of residue prior to addition of plasticizer.

at about 10 to about 20 mm. of Hg by reacting phosgene with a compound selected from the grou consisting of the corresponding primary organic diamines and their hydrohalide salts in the presence of a low boiling inert organic solvent and thereby forming a crude solution of the corresponding diisocyanate, the improvement which comprises adding a plasticizer to said solution and then fractionally distilling the resulting product to recover its diisocyanate content, said plasticizer being selected from the group consisting of a polycyclic aromatic hydrocarbon, a hydrogenated polycyclic aromatic hydrocarbon and a chlorinated aromatic hydrocarbon which boils at a temperature of from about 270 C. to about 400 C.

2. The method defined in claim 1 wherein the low boiling inert organic solvent is substantially completely removed from the crude solution of organic diisocyanate prior to the addition of the plasticizer.

3. The method defined in claim 1, wherein the plasticizer is a chlorinated biphenyl containing from 21% to 62% by weight of chlorine.

4. The method defined in claim 2, wherein the plasticizer is a chlorinated mixture of 60% biphenyl and 40% distilled high boiler containing about 65% Cl.

5. The method defined in claim 2, wherein the plasticizer is a chlorinated isomeric terphenyl mixture containing 42% Cl.

6. The method defined in claim 2, wherein the plasticizer is a chlorinated diaryl mixture boiling from about 270 C. to about 400 C.

7. The method defined in claim 2, wherein the 6 plasticizer is a hydrogenated terphenyl boiling in the range of about 270 C. to about 400 C.

8. The method defined in claim 2, wherein the plasticizer employed is a partially hydrogenated hydrocarbon liquid mixture characterized by having a specific gravity of 1.05 to 0.955 at 25 C. and obtained by the partial catalytic hydrogenation of the mixture of normally solid hydrocarbons boiling about 350 C. at 760 mm.- pressure and formed in the synthesis of biphenyl in the pyrolysis of benzene at elevated temperatures.

9. The method defined in claim 2, wherein the plasticizer is used in an amount varying within the limits of about 5% to about 100% by weight, basis organic diisocyanate content of the crude solution of diisocyanate.

10. The method defined in claim 2, wherein the plasticizer is used in an amount varying within the limits of about 5% to about 50% by weight, basis organic diisocyanate content of the crude solution of diisocyanate.

11. The method defined in claim 2, wherein the plasticizer is used in an amount varying within the limits of about 10% to about 25% by weight, basis organic diisocyanate content or the crude solution of diisocyanate.

References Cited in the file 01 this patent UNITED STATES PATENTS Number Name Date 2,071,932 Macht Feb. 23, 1937 2,223,171 Gaylor Nov. 26, 1940 2,374,340 Farlow Apr. 24, 1945 

1. IN THE METHOD OF PRODUCING ORGANIC DIISOCYANATES BOILING FROM ABOUT 70* C. TO ABOUT 175* C. AT ABOUT 10 TO ABOUT 20 MM. OF HG BY REACTING PHOSGENE WITH A COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE CORRESPONDING PRIMARY ORGANIC DIAMINES AND THEIR HYDROHALIDE SALTS IN THE PRESENCE OF A LOW BOILING INERT ORGANIC SOLVENT AND THEREBY FORMING A CRUDE SOLUTION OF THE CORRESPONDING DIISOCYANATE, THE IMPROVEMENT WHICH COMPRISES ADDING A PLASTICIZER TO SAID SOLUTION AND THEN FRACTIONALLY DISTILLING THE RESULTING PRODUCT TO RECOVER ITS DIISOCYANATE CONTENT SAID PLASTICIZER BEING SELECTED FROM THE GROUP CONSISTING OF A POLYCYCLIC AROMATIC HYDROCARBON, A HYDROGENATED POLYCYCLIC AROMATIC HYDROCARBON AND A CHLORINATED AROMATIC HYDROCARBON WHICH BOILS AT A TEMPERATURE OF FROM ABOUT 270* C. TO ABOUT 400* C. 